This invention relates to mechanisms for preventing overfilling of liquid storage tanks, particularly but not necessarily exclusively underground tanks of the type commonly used by automobile service stations and similar establishments for the storage of gasoline and similar liquid products.
Overfilling storage tanks with gasoline or similar liquids may have detrimental ecological and other consequences. In recognition of this fact, it has been previously proposed to provide mechanisms for automatically stopping or at least retarding the introduction of additional liquid into a tank after it has been filled to a preselected extent, which may be and now normally is dictated by governmental regulations, of its maximum capacity. In order to prevent tampering and/or damage from accidental impacts or the like, the overfill mechanism preferably is located entirely within the tank, in series with the "drop tube" or other conventional piping through which the liquid is introduced into the tank. Retrofit installation of an overfill mechanism located within the tank requires that the mechanism be sufficiently small, especially in its transverse dimension, as to be capable of passage through the tank's inlet opening and the fill pipe normally associated therewith. Many of the prior overfill prevention mechanisms include at least one float that projects laterally from the main body of the mechanism and undergoes arcuate pivotal movement in response to changes in the liquid level within the tank. Mechanisms having float and associated linkage components permanently projecting laterally from the housing of the mechanism cannot be installed readily, if at all, within existing tanks since they will not pass through the tank's inlet opening and/or associated piping. Even those mechanisms having float and linkage components that deploy outwardly from the housing only after passage into the tank will not function properly, if at all, when a side wall or baffle of the tank intersects and obstructs the intended path of pivotal movement of the float. Additionally, and in all cases, the use of long interconnecting linkages between the floats and the components connected thereto significantly increases the cost of the overfill mechanisms, and the risk of component malfunction.
Another undesirable feature of many overfill mechanisms is that they have bleed ports which permit the introduction, albeit at a slow rate, of an unlimited amount of additional liquid into a tank following closure of the main control valve of the mechanism.